Allow docs to be built with Sphinx 1.7.1+ (#8500)
Allow docs to be built with Sphinx 1.7.1+ (#8500)

* Allow docs to be built with Sphinx 1.7.1+

* Allow docs to be built with Sphinx 2.0+

matthiasdiener/spack,krafczyk/spack,matthiasdiener/spack,iulian787/spack,krafczyk/spack,mfherbst/spack,matthiasdiener/spack,matthiasdiener/spack,LLNL/spack,LLNL/spack,iulian787/spack,krafczyk/spack,LLNL/spack,krafczyk/spack,LLNL/spack,mfherbst/spack,LLNL/spack,iulian787/spack,mfherbst/spack,iulian787/spack,mfherbst/spack,matthiasdiener/spack,iulian787/spack,krafczyk/spack,mfherbst/spack